The present invention relates to an exhaust gas pressure regulator for an engine. More particularly, the present invention relates to an exhaust gas pressure regulator having a moveable regulating member for controlling the exhaust gas through flow. Exhaust gas pressure regulators may be used for controlling a back-pressure in the exhaust system, thereby enabling controlled engine braking. The exhaust gas pressure regulator of the invention, can be implemented in the exhaust system for combustion engines configured to be installed in for example heavy-duty vehicles, such as trucks, buses, working machines and construction equipment, but also other types of vehicles, such automobiles.
Combustion engines, in particular piston engines, may be provided with an exhaust gas pressure regulator for allowing exhaust brake functionality. Generally, by restricting or prevention exhaust gas to flow out from the exhaust system the exhaust gas pressure upstream the exhaust gas pressure regulator will increase. As a result, the high-pressure exhaust gas within the exhaust system will generate a relatively large counter force on the top side of the pistons during the exhaust stroke of the piston, such that the combustion engine is forced to slow down.
US2009217662 describes an example of an exhaust gas pressure regulator having a moveable piston arranged in a diffuser duct for controlling the back-pressure in the exhaust system upstream of the regulator.
While the solutions found in the prior art work well in some situations, there is still room for improvements relating to the exhaust gas pressure regulator.
For accomplishing an engine braking effect by means of the gas pressure regulator shown in US2009217662, a regulating pressure source will be connected to an inner piston chamber for forcing a control piston towards its closed position. Upon closure of the control piston a built up pressure on a regulator inlet end will result in increased gas pressure upstream the piston. The pressure will more or less simultaneously increase also inside a chamber formed inside the cone due to the pressure equalising channel 50. The pressure increase will thus act on the piston and cause the piston to move back towards its open position. As a result, increased gas flow past the piston will occur, such that the pressure on the regulator inlet end will drop. Upon reduced gas pressure on the regulator inlet end a regulating pressure of the exhaust gas pressure regulator again will force the control piston towards its closed position. Such pressure variations will cause the control piston to move back and forth rapidly and the amplitude of the oscillations may become particularly large at those engine combustion frequencies that are associated with the resonance frequency of the control piston. One example problem caused by large amplitude oscillations of the control piston is damages to control piston and/or regulator housing caused by repeated impact between the control piston and regulator housing at the end stroke of the regulator piston. Moreover, the oscillation may cause impact between neighbouring laps of a spring coils, thereby resulting in a relaxation problem of the spring and finally fracture damages. Finally, if a dampening element is provided for dampen said impact, the dampening element itself may become damaged due to the large amplitude oscillations.
Consequently, it is desirable to provide an improved exhaust gas pressure regulator in terms of reliability and reduced risk for damages.
The exhaust gas pressure regulator according to an aspect of this disclosure is suitable for a combustion engine and comprises a regulator housing and an inner diffuser assembly arranged inside the regulator housing so that an exhaust gas flow duct is formed between an inner surface of the regulator housing and an outer surface of the inner diffuser assembly. The inner diffuser assembly includes a front portion and a regulating piston that is moveable relative to the front portion and the regulator housing between an idle position in which the exhaust gas flow duct is open, and a pressurized position in which the regulating piston at least partly closes the exhaust gas flow duct. The inner diffuser assembly comprises at least one throttled flow passage between the gas flow duct and an exhaust gas pressure chamber defined by the regulating piston and an interior surface of the front portion.
This set of features ensures that the pressure within the exhaust gas pressure chamber does not oscillate with the same amplitude as the pressure within the gas flow duct. Since part of the effective surface area of the regulating piston accessible by exhaust gas for exerting an axial force on the regulating piston towards the outlet of the regulating housing does no longer experience the high amplitude oscillations, i.e. the part of the regulating piston defining the exhaust gas pressure chamber, the amount of effective surface area of the regulating piston accessible by high amplitude oscillating exhaust gas for exerting an axial force on the regulating piston towards the outlet of the regulating housing is reduced.
In short, the regulating piston effective surface area which is affected by the large pressure oscillations is decreased, and since the axial force exerted on the regulating is proportional to the effective surface area, the oscillating force on the regulating piston is reduced. Thereby, there is less risk for high amplitude oscillations of the regulating piston, and consequently also less risk for damages to the regulating piston, the housing, the spring or and damper element.
Further advantages and advantageous features of the invention are disclosed in the following description.
According to one example aspect of the exhaust gas pressure regulator, the at least one throttled flow passage is configured to form a low-pass filter for stopping high-frequency pressure pulses from reaching the regulating piston 130, but allowing pass of low-frequency pressure pulsations. The low-pass filter enables the average pressure within the exhaust gas pressure chamber 132 to follow the average pressure of the exhaust gas within any of the exhaust gas duct 106.
According to a further example aspect of the exhaust gas pressure regulator, the front portion is stationary arranged in the regulator housing. A stationery front portion with an internally arranged regulating valve enables less effective surface area accessible by the high amplitude pressure oscillations in the exhaust gas stream, such that the regulating piston will less likely be damaged due to osculating impacts against the regulating housing at the end positions.
According to a further example aspect of the exhaust gas pressure regulator, the at least one throttled flow passage is configured such that an average pressure level within the exhaust gas pressure chamber corresponds substantially to an average exhaust gas pressure level of the exhaust gas stream at an inlet to the throttled flow passage. With too little throttling effect of the throttled flow passage substantially no pressure averaging effect is obtained by the throttled flow passage, such that relatively large amplitude pressure oscillations will propagate into the exhaust gas pressure chamber and potentially cause the regulating piston to oscillate with high amplitude. With too high throttling effect an increase in backpressure at the inlet of the exhaust gas pressure regulator caused by a suddenly closed regulating piston may result in a relatively slow increase of the pressure within the exhaust gas pressure chamber, such that the regulating piston too slowly will reach its equilibrium position. This delay in reaching the equilibrium position might therefore generate excessive back pressure for a certain time period, such that the vehicle brake effect is higher than desired.
Moreover, with too high throttling effect it may also become difficult to quickly change the position of the regulating piston at all, such that a desired backpressure at the inlet of the exhaust gas pressure regulator may temporarily significantly deviate from the actual back pressure. Such deviation is undesirable because it implies that the engine braking system does not provide as much braking force as desired. Consequently, either the hydraulic braking system must temporarily compensate for lack of braking force by means of complex regulating systems, or the driver will experience an undesirable inconsistency between vehicle deceleration and brake pedal actuation.
According to a further example aspect of the exhaust gas pressure regulator, a total throttled flow passage of the diffuser assembly has a flow area in the range of 0.5-10 mm2, specifically in the range of 1-6 mm2, more specifically in the range of 2-4 mm2. These ranges are deemed appropriate for enabling a balance between risk for regulator damages and delay of engine brake performance at transient conditions.
According to a further example aspect of the exhaust gas pressure regulator the total throttled flow passage is configured such that a degree of pressure attenuation of the high frequency components of the dynamic pressure pulsations in the exhaust gas flow duct is at least −6 dB, specifically at least −10 dB, and more specifically at least −20 dB. As discussed above, too high attenuation may result in reduced consistency between desired braking performance and actually delivered engine braking performance, and too low attenuation may result in damages to the regulator. A −6 dB attenuation of the amplitude of the pressure pulsations of the exhaust gas stream means that the amplitude of the pressure pulsations in the exhaust gas pressure chamber is reduced by half. A −10 dB attenuation means that the amplitude of the pressure pulsations in the exhaust gas pressure chamber are reduced by about three times, and a −20 dB attenuation means that the amplitude of the pressure pulsations in the exhaust gas pressure chamber are reduced by ten times.
According to a further example aspect of the exhaust gas pressure regulator, the inner diffuser assembly comprises a sealing ring that is configured to at least partly seal a flow passage between the regulating piston and the front portion of the inner diffuser assembly so that the at least one throttled flow passage is provided by means of a calibrated flow leakage past the sealing ring. By using the existing sealing ring as throttled flow passage no significant modifications of the regulator must be performed for implementing the solution of the disclosure. The sealing ring also has the advantage of enabling easy calibration of the throttling capacity merely by selecting a specific sealing ring. For example, by using a split piston ring that is located in a groove, the flow passage past the sealing ring is easily adaptable by varying the gap between the ends of the split piston ring in assembled state.
According to a further example aspect of the exhaust gas pressure regulator, the sealing ring is a metal piston ring. See advantages mentioned above.
According to a further example aspect of the exhaust gas pressure regulator, the metal piston ring in a mounted state has a gap between the circumferential ends of the piston ring. See advantages mentioned above.
According to a further example aspect of the exhaust gas pressure regulator, a circumferential length of an arc-shaped gap between the circumferential ends of the piston ring is in the range of 2-50 mm, specifically in the range of 3-25 mm, and more specifically in the range of 5-20 mm. These ranges are deemed appropriate for enabling a balance between risk for regulator damages and delay of engine brake performance at transient conditions.
According to a further example aspect of the exhaust gas pressure regulator, the at least one throttled flow passage is provided by means of a calibrated flow leakage through at least one aperture in the front portion of the inner diffuser assembly facing the exhaust gas stream. As an alternative for using the sealing ring for calibrating the flow leakage, an separate flow passage may be provided in the front portion of the inner diffuser assembly facing the exhaust gas stream. The flow passage may be implemented in form of at least one aperture that enables pressure equilibration between the pressure within the gas flow duct and the pressure within the exhaust gas pressure chamber. The aperture may for example be provided by means of drilling a hole in the front portion of the inner diffuser.
According to a further example aspect of the exhaust gas pressure regulator, a total amount of effective surface area of the regulating piston accessible by exhaust gas in the exhaust gas flow duct for exerting an axial force on the regulating piston towards the outlet of the regulating housing is less than 75% of a total amount of effective surface area of the regulating piston accessible by exhaust gas within the exhaust gas pressure chamber for exerting an axial force on the regulating piston towards the outlet of the regulating housing, specifically less than 50%, and more specifically less than 30%. By having only a portion of the total amount of effective surface area of the regulating piston accessible by exhaust gas in the exhaust gas flow duct the axial force that may be exerted by the large amplitude pressure pulsations of the exhaust gas in the exhaust gas flow is reduced compared with a regulator design where the entire amount of effective surface area of the regulating piston is accessible by exhaust gas in the exhaust gas flow duct. Hence, by selecting a regulator design with a large amount of the total amount of effective surface area of the regulating piston located within the exhaust gas pressure chamber, only a small amount of the total amount of effective surface is still available, thereby enabling reduced problem caused by large amplitude pressure pulses in the exhaust gas of the exhaust gas flow duct.
According to a further example aspect of the exhaust gas pressure regulator, the exhaust gas pressure regulator further comprises a control pressure chamber defined by the regulating piston, a nozzle unit and the shaft, wherein a pressurised medium within the control pressure chamber is arranged to exert a force on the regulating piston towards the pressurized position. This arrangement enables a reliable and cost-efficient control of the regulating position of the regulator piston.
According to a further example aspect of the exhaust gas pressure regulator, the pressure regulator further comprises a pressure medium flow passage for supplying pressurised medium from an outside pressure medium source to the control pressure chamber. Thereby, the regulating position of the regulator piston may be controlled by an externally arranged control unit, a pressure medium source and a suitable valve arrangement.
According to a further example aspect of the exhaust gas pressure regulator, the front portion of the inner diffuser assembly has a closed end facing an exhaust gas flow inlet of the exhaust gas pressure regulator, and an open end facing an exhaust gas outlet of the exhaust gas pressure regulator, wherein an annular damping member is provided between an axial abutment surface of the regulating piston and an opposite axial abutment surface of the front portion of the inner diffuser assembly for damping impact forces between the regulating piston and the front portion of the inner diffuser assembly. The annular damping member serves to dampen the impact of the regulating piston with the front portion of the inner diffuser assembly. Thereby the impact force may be reduced, and if damages occur it is less costly to change a damaged seaming member than changing the regulating piston and/or the regulator housing. The annular damping member may be located in either the regulating piston or the front portion of the inner diffuser assembly.
According to a further example aspect of the exhaust gas pressure regulator, front portion of the inner diffuser assembly has a conical shape with a generally increasing outer diameter in the axial direction from the closed end towards to the open end, and the opposite axial abutment surface of the front portion of the inner diffuser assembly is located in a radially outer region located near or at the open end. By providing the abutment surface relatively far out from a centre axis of the housing, in a radial direction, a relatively large abutment surface of the annular damping element is provided for a certain damping element width, because the area of the abutment surface is A=π(ro2-ri2), where or corresponds to the outer radius of the annular damping element and rig corresponds to the inner radius of the annular damping element.
According to a further example aspect of the exhaust gas pressure regulator, the annular damping element is a metal textile bushing. This type of material is sufficiently heat resistant for being located in the exhaust pressure regulator.
According to a further example aspect of the exhaust gas pressure regulator, both an internal cross-sectional area defined by the inner surface of a regulator housing and an outer diameter of the inner diffuser assembly increases in an axial direction towards an outlet of the exhaust gas pressure regulator, and the diffuser assembly is arranged concentrically inside the inner surface of a regulator housing. The shape of the regulator housing is in particular suitable for being placed upstream of the rotor of an axial turbine because the exhaust gas flow is modified for hitting the blades of the axial turbine.
According to a further example aspect of the exhaust gas pressure regulator, the regulating piston is urged towards the idle position by the force of a mechanical spring device. Thereby, it is ensured that the regulating piston does not accidentally close the flow path of the exhaust gas flow.
According to a further example aspect of the exhaust gas pressure regulator, the regulating piston comprises a sleeve portion in sliding contact with an exterior side of the front portion of the inner diffuser assembly, and the sleeve portion protrudes into the exhaust gas flow duct when the regulating piston is in the pressurized position for at least partly closing the exhaust gas flow duct. Using the sleeve portion for closing the flow path of the exhaust gas flow in the exhaust gas flow duct has the advantage of reducing the effective surface area of the regulating piston that may generate an axial force on the regulating piston towards the closed position. Thereby, any large amplitude pressure pulses within the exhaust gas flow in the exhaust gas flow duct will not transmit any large forces for moving the regulating piston in the axial direction.
According to a further example aspect of the exhaust gas pressure regulator, the diffuser assembly comprises a stationary shaft, and the regulator piston is slidingly arranged on the shaft. This arrangement enables a robust design of the gas pressure regulator.
The disclosure further includes an exhaust gas system for an internal combustion engine comprising a gas pressure regulator as described above located downstream of a first turbine unit and upstream of a second turbine unit.
According to an example aspect of the exhaust gas system, the diffuser assembly forms a nozzle for the second turbine unit.
According to a further example aspect of the exhaust gas system, the second turbine unit is a turbo-compound unit.
According to a further example aspect of the exhaust, gas system, the first turbine unit is a turbo-charger unit.
The disclosure further includes a combustion engine comprising an exhaust gas system as described above.
The disclosure further includes a vehicle comprising a combustion engine as described above.